In 2023, lots of classic stories will have their copyrights expire and will enter the public domain, including the last of the Sherlock Holmes stories from Sir Arthur Conan Doyle. This allows new opportunities for various content creators to use the newest additions to the public domain for their own purposes.
The public domain has always been an interesting and complicated topic, especially when it comes to characters with disputed licensing behind them. But other characters, such as various mythological deities and legendary heroes, have made appearances in both DC Comics.
Hercules
The easiest public domain characters to use in Marvel and DC are mythological gods and demigods from several hundred years ago. And one of the biggest names that has been used is the Greek god Hercules.
While Hercules does appear in DC Comics as well, he is known far more for his role in Marvel Comics. Both interpretations of the character show him as a superstrong warrior with a love for combat. But while DC's Hercules isn't used that often, Marvel's version of the character is much more involved with the major events of the franchise, and has even saved the planet and the entire universe at one point.
Dracula
Dracula is involved in several of the best gothic monster movies, and has appeared as an antagonist to both mainline and supernatural heroes in both comic lines.
While Dracula in DC is most famous for the Batman: Red Rain trilogy in which he battles with Batman, Dracula in Marvel is, of course, known for being a nemesis for Blade. But both follow the basic idea of Bram Stoker's original Dracula novel, making Dracula the leader of the vampires and a big threat no matter who fights him. He's not as often of a threat, but still a noticeable one, especially when he makes big plays for world domination.
Sherlock Holmes
There are many great Sherlock Holmes movies, but compared to some of the other public domain characters, he hasn't been there long. However, that hasn't stopped both Marvel and DC from using Sir Arthur Conan Doyle's legendary detective.
He hasn't had many appearances in DC, especially in recent days, but he did encounter both Hawkman and Batman at different points. While Marvel published their own comic line for Sherlock decades ago, perhaps one of his most well known appearance was in Deadpool Killistrated, in which he forms a team of other classic/public domain characters to stop an evil Deadpool from destroying the Ideaverse.
Frankenstein's Monster
Despite being seen as a villain by many in the source material, Frankenstein's monster has been depicted as a hero in both Marvel and DC.
In Marvel, Mary Shelly's creation, along with the many times he's been cloned, has been friends with Elsa Bloodstone and has worked for the Howling Commandos, being a powerful ally for the heroes. As for his DC counterpart, he is seen as a powerful warrior and actually a strong ally to have. After all, as seen in Final Crisis, Frankenstein is immune to the Anti-Life Equation due to already being dead.
Robin Hood
Robin Hood is a legendary archer from hundreds of years ago in English lore, making it tough for him to be used despite being in the public domain. But, thanks to time travel, both Marvel and DC have been able to pull it off.
Marvel's Robin Hood has been the subject of some debate on his true identity. Some say that he is a time traveling Hawkeye, while others claim that he's actually the Asgardian Fandral. But for DC, Robin Hood is definitely his own person and has helped out the heroes several times, most notably Green Arrow and Speedy, and has met other time travelers like Rip Hunter.
Thor
Thor is one of Marvel's heaviest hitters, and has taken down some of Marvel's most powerful characters. But because of his Norse origins, the character actually comes from the public domain.
While Thor does also exist in DC Comics, that version pales in comparison to the popularity of Marvel's iteration of the character. Marvel's Thor is iconic and has ed multiple teams including the Avengers. Not only that, but he's saved all of existence several times. While Marvel's Thor has deviated from the original character, the mythology is still there, serving as a basis for the Marvel character's origins.
Abraham Van Helsing
Throughout all the best adaptions of classic horror monsters, where there has been Dracula, there has been Abraham Van Helsing to fight him. And this is also true in the comics.
DC's Van Helsing is not much to talk about, with very few major appearances, especially after Crisis on Infinite Earths. But Marvel's Van Helsing is more fleshed out and served as a better nemesis for Dracula in the early days of both their appearances. This Van Helsing even worked alongside the villain Apocalypse a few times, but would eventually be ambushed and killed by Dracula himself.
Medusa
Medusa is one of Wonder Woman's deadliest foes in DC, but the mythological gorgon has also appeared in Marvel Comics as well.
Marvel's Medusa Gorgon (not to be confused with Medusa, queen of the Inhumans), functioned much like both the DC version and the original Greek myth, being that she could turn people to stone that looked at her. Both Medusas also tended to fight characters with ties to Greek mythology as well, with the DC version being an enemy of Wonder Woman and the Marvel version being an enemy of Hercules.
Ares
As the Greek god of war, it makes sense that Ares would be involved in some of the biggest conflicts in Marvel and DC's history, although the DC version seems both more accurate and powerful than his Marvel counterpart.
In DC, Ares is a god in the literal sense, being fueled by conflict. The more conflict and war there is, the stronger he gets. The Ares in Marvel, however, at times seems nothing more than a brute. Though he is still a god and is associated with the other Greek gods in Marvel, he is still often bested, especially when he is pitted against the likes of Thor and the Avengers.
Loki
Like Thor, Loki originally comes from Norse mythology, making him fair game for Marvel and DC to use thanks to public domain.
Loki's DC form, however, barely shows up anywhere beyond certain comics like Sandman. Marvel's Loki, however, is one of the most iconic villains in the company's history. The character perfectly shows off the mischievous side of the character, using trickery and deception to move forward with his plans and goals, and even being able to fool the most intelligent and careful of characters. It's not wonder why he's the God of Mischief.